Method of and means for measuring unbalance



Oct. 23, 1923. 1,471,383

' A. B. CLARK METHOD OF AND MEANS FOR MEASURING UNBALANCE Filed Oct. 151919 INVENTOR ATTORNEY Patented Oct. 23, 1923.

UNITED STATES PATENT OFFICE.

ALVA B. CLARK, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

METHOD OE AND MEANS FOR MEASURING UNBALANCE.

Application filed October 15, 1919. Serial No. 330,812.

To all whom it may concern:

Be it known that I, ALVA B. CLARK, re-" siding at Brooklyn, in thecounty of Kings and State of New York, have invented certainImprovements in Methods of and Means for Measuring Unbalance, of whichthe following is a specification.

This invention relates to methods of and means for measuring theunbalance between a pair of electrical devices, such as a telephone lineand its network.

The closeness of the balance between a line and its network is of highimportance in the telephone and telegraph art, because certain apparatusis limited in effectiveness by the extent of the unbalance between theline and network associated therewith. The maximum permissibleamplification or gain of a repeater, for example, is limited by theamount of unbalance between the line and network.

The amount of the unbalance must con sequently be measured often.Heretofore this was usually done by making impedancemeasurementsseparately on the line and the network, and plotting theresults as curves for purposes of comparison. This method wasexceedingly tedious, and it is the object of this invention to provide amethod and means whereby the unbalance at any frequency may bedetermined by a single measurement.

In this invention the line and network are connected in series with eachother in the secondary circuit of a transformer, in whose primarycircuit there is a source of current of variable frequency. If the lineand network are in perfect balance, i. e.,if their impedance are exactlyalike, the drop of voltage in the line is the same as the drop in thenetwork, so that'the midpoints of the secondary circuit are of the samepotential and no current flows through a circuit connected to the saidmidpoints. When there is an unbalance, however, current enters the said.circuit, the strength of this current dependingupon the extent of theunbalance.

The combination of the'transformer with the line and network thisconstitutes a circuit arrangement which transmits a certain value ofcurrent to the circuit associated with the said midpoints, according tothe extent of 'the unbalance between the line and the network. Thetransmission efficiency of this combination thus serves as a measure ofthe unbalance. In telephone practice it is customary and convenient toexpress the transmission efliciency of any apparatus in terms of thenumlber of miles of standard cable having like efliciency. The measuringapparatus of this invention is therefore so arranged that the transmission efliciency of the combination above referred to may beascertained in terms of the number of miles of cable to which thecombination is equivalent or, simply, the

the maximum amplification of, the repeater in miles. The measuringapparatus of this invention may be so arranged that the said. value ofseven miles is automatically deilucted from the true transmissionequivaent. I

A good understanding of the invention may be had from the followingdescription thereof considered in connection with the accompanyingdrawing showing in Figure 1 a diagrammatic view of one form andarrangement of apparatus embodying the invention, and in Fig. 2, amodification of a portion of said apparatus.

In Fig. 1 reference characters L and N- designate the line and networkrespectively, the unbalance between which is to be de: termined. Athree-winding transformer '30 is provided for associating the line andnetwork in ba ancing relationship during the test, the arrangement ofthe windings of the transformer being such that current flowing in theprimary winding Causes 2. flow of current through the line and networkin series, so that the midpoints 31. of the secondary windings are atthe same potential provided the network and line have the sameimpedance, that is, are in perfect balance.

The difference between the potentials of the midpoints is thus a measureof the unbalance between the impedance of the line and the impedance ofthe network, at the frequency under test. The transformer thus transmitsfrom the source associated with the primary to a circuit connected tothe m'dpoints of the secondary, a value of current determined by theextent ot the unbalance between the line and the network. Thetransmission efiiciency of this arrangement constitutes, therefore, ameasure of the unbalance, as hereinbelore explained. The apparatusdescribed below is so arranged that-this eiiiciency may be ascertainedin the number oi miles oi standard cable equivalent thereto, it beingunderstood,however, that the apparatus may readily be so modified thatthe unbalance may be ascertained in other units.

The transmission measuring apparatus comprises a source of alternatingcurrent variable in frequency, preferably an oscillator, associated withthe primary of a transformer 5, the secondary circuit of which comprisesresistances 6 and 7 in series with each other. A switch 8 is providedfor associating the tenninals of the resistance 7 and a measuringcircuit M with the primary side of the transformer 30 and the midpoints31. In the case shown in Figure 1 the resistance 7 is associated withthe primary of the transformer 30 and the measuring circuit M with themidpo-ints 31 of the secondary. Current proportional to the intensityoil the source is thus impressed on transformer 30 and current, of avalue determined by the transmission equivalent of the combination ofthe transformer with the line and the network, flows into the measuringcircuit M. This circuit comprises an adjustable impedance device 9,preferably an artificial li e, the transmission equivalent of which maye varied by means of dials 10 and ll. The current which passes throughthe device 9 is impressed by a potentiometer 12 on an amplifying element17, the output current of this element being rectified by an electrontube 13 and caused to flow through a resistance 15. The drop inpotential in this resistance depends upon the strength of the source 32,and to render the indicating device in the present arrangementunatlected thereby, T provide a like resist: ance 15 which is traversedby current from. a rectifier 13 associated by reference ci cuit lit withthe resistance Resistances and 15 are connected to eac end and associacil at the oth r enc, this galv to indicate when the current in oneresistance is equal to the current in the other. Condensers 18 and 18are connected in parallel with the resistances to improve the aclion ofthe galvanometer. A resistance 50 and condenser 51 are included in thereference circuit to make the transmission characteristics of thecircuit equal to that oil the measuring circuit at all essentialfrequencies, it being understood, however, that any other suitabledevice may be used for this purpose.

The transformer 30 may at times be disconnected from the apparatus byreversing switch 8, connections 40 being provided between the lowerterminals of the switch to connect the measuring circuit directly toresistance 7 so that the full value of the current is impressed oncircuit M for purposes of calibration, as I shall now explain.

To calibrate the measuring circuit, switch 8 is thrown to its lowerposition so that the circuit M is in direct connection with theresistance 7. The source of current is then regulated to give thedesired frequency and the dials 10 and 11 are turned to the position atwhich the artificial line 9 causes a maximum loss of transmission incircuit M. Potentiometer 12 is then adjusted until the currentflowing-through the resistances l5 and 15 are equal, as indicated by thepointer of the galvanometer standing at zero.

To make a measurement of the unbalance between the line and the network,switch 8 is thrown to close its upper contacts, so that the current fromthe source is impressed on the transformer 30 and only such currententers circuit M as is caused by the dil'lerence in potentialbetweempoints 31 owing to the unbalance between' the line and thenetwork. The current which now flows through resistance 15 is less thanthe current which flowed therethrough during the calibration of theapparatus, so that the galvanometer needle is thrown oil its zeroposition. The transmission equivalent of line 9 is then reduced byrotating the dials l0 and 11 until the current in the measuring circuitis restored to its prior value, as indicated by the return of thegalvanometer needle to its middle position. The dials lt and ll arecalibrated to indicate the number of miles by which the equivalent ofthe artificial line has been reduced, this quantity being equal to thetransmission equivalent of the transformer with the line and thenetwork.

This equivalent, as explained hereinbei ore, is a measure of theunbalance between t line and networlr under test, the greater the valueof the equivalent the smaller losing the extent of the unbalance. Thevalue uivalent moreover, has an impor practic significance, for whenreducer seven 4 file", it represents the lowable amplification or gain(in miles) of a repeater associated with the line and network.

In a modification of the apparatus, the said quantity of seven miles isautomatically deducted from the transmission equivalent. Thismodification is illustrated in Fig. 2, the arrangement therein shownconnected to terminals a, b, c, d, being intended to be substituted inFig. 1 for the circuit connected between terminals (1, b, c, and d. Thethree winding transformer 30 of Fig. 2 is then directly connected to theresistance 7 and the midpoints of this transformer are in directconnection with the artificial line 9. Switches 43 and 44 associatedwith the secondary terminals of the transformer are provided for attimes connecting line L and network N with the transformer and at othertimes impedance devices n and l which are here shown as simpleresistances. These devices are of unequal magnitude and so proportionedthat they introduce a loss of transmission between terminals a, c, and

b, d, equal to about seven miles, when switches 43 and 44 are thrown tothe left. The calibration of the circuit is made with resistance n and Zconnected to transformer 30 so that when the unbalance measurement issubsequently made on line L and network N the dials indicate directlyseven miles less than the actual equivalent thereof.

The apparatus of this invention is practically independent of currentstrength because of the use of the reference circuit for balancing theeffect of current in the measuring circuit audit is also substantiallyindependent of the frequency of the current, the amplifier beingdesigned to be as distortionless as possible throughout the entire rangeof frequencies. Thus a single calibration at a frequency of, say, 800cycles, is sufficient even though measurements are made throughout awide range of frequencies, and the strength of the source need not beheld constant throughout the test. The manner in which the value of thecurrent in the measuring circuit is compared with the value of thecurrent in the reference circuit, is applicable to many other branchesof the electrical art. In this aspect, the invention consists inrendering the null method broadly applicable to measurements made withalternating cur rents, this method heretofore having been capable,generally, of use only in measurements with direct currents oralternating currents of like phase, as for example in the D. C. andffta.C. bridges.- By rectifying the currents before impressing them on thegalvanometer the measurement is rendered independent of the relativephases of the currents, or even of their relative frequencies.

Although only two forms of apparatus 1 embodying the invention are shownand detween the scribed herein it is readily understood that variouschanges and modifications may be made therein within the scope of thefollowing claims without departing from the spirit and scope of theinvention.

What is claimed is: Y

1. The method of determining the extent of the unbalanceat any frequencybetween a pair of electrical devices, which consists in associating saiddevices in series relation with a source of current having saidfrequency and indicating the difference bepotential drops in the saiddevices.

2. The method of ascertaining the extent of unbalance at any frequencybetween a pair of electrical devices, which consists in connecting saiddevices in a circuit in series relation with a source of current of saidfrequency and obtaining an indication of the value of current in abranch circuit as sociated with the said circuit at points midwaybetween said devices, as compared with the value of current in saidbranch circuit when said source is connected directly therewith.

3. The method of determining the'extent of the unbalance between a pairof electrical devices, whichconsists in determining the reduction'in thetransmission equivalent of a circuit by interposing said devices inbalanced relation in said circuit.

4. The method of measuring unbalance between a line and its balancingnetwork, which consists in 'interposing the points of balancebetween-them in a measuringcircuit and applying current from a sourcethrough a transformer to the line and the network in series, and cuttingout calibrated standard miles in said measuring circuit until thecurrent therein is restored to the value it had as compared with whenthe source was applied directly to the measuring circuit.

5. The method of determining the extent.

of unbalance existing between a pair of electrical devices, whichconsists in connecingsaid devices in series with the secondary circuitof a transformer, applying a source of current to the primary of saidtransformer. and ascertaining the value of current caused thereby in acircuit associated with points midway between said devices, as comparedwith the current in said circuit when said source is applied directlywithout the interposition of saidtransformer and said devices.

6. The method of ascertaining the extent of unbalanceexisting between aline and a network, which consists in connecting said line and networkin series with the secondary winding of a transformer, and" ascertainingthe transmission equivalent from a source through the primary of saidtransformer to the midpoints of the secondary an indication of &

circuit, as compared with the transmission equivalent when said line andnetwork and transformer are omitted and connection is made directly fromsaid source to the conductors formerly connected with said midpoints.

7. The method of determining the extent of the unbalance at anyfrequency between a pair of electrical devices, which consists incausing a flow of current of said frequency through said device's,causing a current determined by the unbalance which exists between themto flow through a measuring circuit. causing a current determined by theintensity of the current in the. said devices to flow through areference circuit, and adjusting the relative transmission of saidmeasuring and reference circuits until the currents therein havepredetermined relative values.

8. The method of determining the extent of the unbalance between a pairof electrical devices. which consists in causing a flow of currentthrough said devices, causing a flow of current determined by theunbalance which exists between them to flow through a measuring circuitand adjusting the transmission of said circuit until the currenttransmitted thereby has a predetermined value relative to the intensityof the current caused to flow through said devices.

9. The method of determining the extent of the unbalance between a pairof electrical devices which consists in causing a flow of currentthrough said devices, causing a current determined by the unbalancewhich exists between them to flow through a measuring circuit, adjustingthe transmission of said measuring circuit to a predetermined value, andascertaining the extent of the change in the transmis ion of saidcircuit.

10. The method of determining the unbalance between a 'pair ofelectrical devices, which consists in applying a source of current to ameasuring circuit, then applying said source. to said devices andcausing a flow of current in the measuring circuit determined by thediilerence between the impedances of said devices and determining therelative intensities of'said currents in said circuits.

11. The method of determining the extent of the unbalance at any"frequency between a pair oi electrical devices which consists inapplying a source of current of said "frequency to a measuring circuitand adjusting the transmission of said circuit to a preassigned value,then applying said source to a circuit comprised of said devices associated with each other in balancing relationship and cruising currentdetermined by the extent or the unbalance between said devices to saidmeasuring circuit, ad- 4 nsmission equivalent of said eiativeiy to saidpie-assigned value,

amines and ascertaining the extent of the change in the value of saidtransmission equivalent.

12. The method of determining the transmission equivalent of anelectrical device which consists in causing a flow of current thnough ameasuring circuit to actuate an indicating device in one direct-ion,causing flow of-current through a-reference circuit to actuate saiddevice in the opposite direction, adjusting the relative value ofcurrents actuating said indicating device to a predetermined value,connecting said first mentioned device in tandem with said measuringcircuit, adjusting the transmission equivalentof said circuit until theindicating device is restored to its previous'position and ascertainingthe extent of the change in the transmission equivalent of said circuit.

13. The method of determining the maximum permissible gain of theamplifying element of a repeater to be associated with a certain lineand network, which consists in associating a source of current with ameasuring circuit, interposing between said circuit and said source adevice for causing a predetermined loss in transmission, adjusting thevalue of current transmitted by said measuring circuit to apredetermined 'alue relative to the current flowing from said source,removing said device and substituting therefor said line and networkassociated in balancing relationship so that a current determined by theextent of the unbalance between said line and network enters saidmeasuring circuit, adjusting the transmission equivalent of saidmeasuring circuit until the current leaving said measuring circuit isrestored to its previous value and ascertaining the extent of the changein transmission of said circuit.

14. The method of determining the transmission of an electrical device,which consists in impressing current from a source of variable frequencyon a current responsive device to actuate the same in one direction,simultaneously impressing current from the same source on a circuit orvariable transmission and causing the current transmitted thereby toactuate said responsive device in the other direction. varying thecurrent applied to said translating device to balance the forcesactuating the same in opposite directions, connecting the unknown linein tandem with said known circuit, changing the transmission equivalentoft the latter to restore balance of the translating device, andascertaining the extent oi. the change in the equi alent of said device.

15. In apparatus for determining the unbalance between a pair electricalde' vices, means for associating said devices in balancing relati nship.means for applying current at var' is frequency thereto, cir-= cuitiorreceiving the current to unbalance between the said devices, and meansfor determining the amount of said current rela tive to the currentapplied to said line and network.

16.-In an apparatus for determining the amount of unbalance existingbetween a pair of electrical devices, a source of current, a measuringcircuit, means governed by said devices in accordance with the amount ofunbalance existing therebetween for applying current from said source tosaid measuring circuit, a reference circuit also supplied with currentfrom said source, .and means for regulating the. relative value ofcurrent in said circuits.

17. In an apparatus for determining the amount of unbalance existingbetween a pair of electrical devices, a source of current, a measuringcircuit, means governed by said devices in accordance with the amount ofunbalance existing therebetween for applying current from said source tosaid measuring circuit, a reference circuit also supplied with currentfrom said source, aniindi'cating device governed by said circuits andresponsive to the values of current therein, and an impedance deviceassociated with one of said circuits for controlling the relative amountof current in said circuits.

18. In an apparatus for determining the.

amount of unbalance existing between a pair of electrical devices, asource of current, a measuring circuit, means governed by said devicesin accordance with the amount of unbalance existing therebetween forapplying current from said source to said measuring circuit, a referencecircuit also supplied with current from said source, a switch for attimes rendering the said devices ineffective to govern the currentapplied from said source to said measuring circuit, and an impedancedevice for controlling the relative value of current in said circuits.

19. In an apparatus for determining the amount of unbalance betweenapair of electrical devices, a source of current, a measuring circuit,means governed'by said devices in accordance with the amountof'unbalance existing therebetween for applying current from said sourceto said measuring circuit, a reference circuit also supplied withcurrent from said source, a switch for at times ren dering the saiddevices ineffective to govern the current applied from said source tosaid measuring circuit, an impedance device for controlling the relativevalue of current in said circuits, and an indicating device governed bysaid circuits and responsive to the relative value of currents therein.

20. In an apparatus for determining the amount of the unbalance betweena pair of electrical devices, a source of current, a measuring circuit,means governed by said devices in accordance with the amount ofunbalance existing therebetween for applyin'g current from said sourceto said measuring circuit, a reference circuit also supplied withcurrent from said source, a switch for at times rendering the saiddevices ineffective to govern the current applied from said source tosaid measuring circuit, an impedance device for governing the relativevalues of current in said circuits when said switch is in one position,a second impedance device for governing the relative values of cur rentin said circuits whensaid switch is in its other position, and anindicating device governed by said circuits and responsive to therelative values of current therein.

21. In an apparatus for determining the amount of the unbalance betweena pair of electrical devices, a source of current, a measuring circuit,a reference circuit supplied with current from said source, anindicating device associated with said circuits and actuated in oppositedirections by the currents therein, a device for governing the amount ofcurrent in said measuring circuit, a switch for at times rendering saiddevice effective to control the amount of current in said measuringcircuit in accordance with the amount of unbalance existing between thesaid pair of electrical devices, an impedance device in said measuringcircuit for governing the current in said circuit to have equal valuesin each position of the switch and means governed by said impedancedevice'for indicating the amount of unbalance between said devices.

22. In an apparatus for determiningthe transmission of anelectricaldevice, the combination of a source of current, a measuring circuitassociated with said source, a referenee circuit associated with saidsource, an indicating device responsive to the relative value ofcurrents in said circuits, means for at times interposing the saidelectrical device between said source and said measuring circuit, andmeans for adjusting the value of current in said measuring circuitrelative to the current in said reference circuit.

23. In an apparatus for determining the transmission of an electricaldevice, the combination of a source of current, a measuring circuitassociated with said source, a reference circuit also associated withthe source, an indicating device actuated in 0pposite directions by thecurrent in said cir-' cuits, means for adjusting the indication of saiddevice to a pre-assigned value, means for connecting tne said electricaldevice into said measuring circuit, means for adjusting the transmissionof said circuit until the indication of said device is returned to saidpre-assigned value, and means for indicating the change in thetransmission of said circuit.

24. The method of determining the value of alternating current in onecircuit relative to the current in another circuit, which consists inrectifying saidcurrents and causing said rectified currents to actuate acurrent responsive device in opposite directions.

25. In combination, a source of alternating current, a first circuitassociated therewith, a translating device, a rectifier for causing thecurrent from said first circuit to actuate said device in one direction,a second circuit also associated with said source, and a rectifier forcausing the current from said second circuit to actuate said device inthe opposite direction. p

26. The method of measuring unbalance between a line and its balancingnetwork, which consists in interposing the points of balance betweenthem in a measuring circuit and cuttin out calibrated standard miles insaid circuit till the current therein is restored to the value it hadbefore the interposition was made.

27. The method of measuring unbalance between two electrical deviceswhich consists in energizing them in a circuit in which they are onopposite sides of two points of equal potential if the balance isperfect, and connecting these two points in another circuit andmeasuring the transmission equivalent a in said other circuit necessaryto compensate for the unbalance.

28. In combination, a transformer with two secondary windings, twoelectrical devices alternately in series with said windings in acircuit, another circuit comprising two points in said secondariesrespectively of equal potential when said two devices are in balance,and calibrated means in said other circuit to measure the actualImbalance of said devices.

29. ltn a circuit for measuring transmission, a path having a calculabletransmission efiiciency, a path comprising apparatus to be tested, avariable resistance in one of said paths for rendering the transmissionthrough said paths equal, and means for passing alternating currentthrough said paths in series.

30. The method of measuring the transmission of electrical apparatus,which comprises sending an alternating current through a path containingsaid apparatus and a second path in series, and adjusting one of saidpaths until the transmission therethrough is equal to the transmissionthrough the other of said paths.

In testimony whereof, I have signed my name to this specification this10th day of October, 1919.

ALVA B. CLARK.

